The present invention relates to image display devices and more particularly to commutators for addressing electrodes in such devices.
Many display devices, such as plasma tubes, electron feedback multiplier devices and guided beam devices, display an image by sequentially addressing various electrodes within the device. For example, many of the devices use about 480 electrodes to select the desired horizontal line of the image to be scanned. This selection requires an addressing circuit for switching various electrical potentials to each of the line select electrodes. One such circuit commonly used in the prior art for biasing the electrodes to one of two potentials (V.sub.1 or V.sub.2) is shown in FIG. 1. The various electrodes 101-104 to be biased are connected to a first voltage V.sub.1 via resistors 106. A second or address voltage V.sub.2 is connected to the electrodes 101-104 via switches, such as transistors 108. The transistors 108 are controlled by a clock circuit 110.
In the non-addressed state, each of the electrodes 101-104 is maintained at the first voltage level V.sub.1 by switching the associated transistor off. Since without current flow there is no voltage drop across the resistor 106, each electrode 101-104 is held at the V.sub.1 potential. To address an electrode 101-104, the associated transistor 108 is turned on by clock 110 so as to connect the electrode to the V.sub.2 potential. However, in this on state, current flows between the V.sub.1 and V.sub.2 voltage sources through the associated resistor 106. Since this current flow serves no function in the display device, it adds unnecessary power consumption to the display. In order to reduce the power consumption, the resistors 106 must have a high value. However, in addiition to the unnecessary power consumption of the circuit 100, when an electrode 102 is switched to the address potential V.sub.2, the switching transient is coupled to the adjacent electrodes 101 and 103 by the interelectrode capacitance 112 inherent in the physical structure of the device. The RC time constant formed by the interelectrode capacitance 112 and the coupling resistors 106 produces a decay time in the transient electric voltages on the adjacent electrodes, during which period the display device may be inoperative. In order to shorten the time constant, the resistors 106 must be a sufficiently small value, thus creating a tradeoff between the decay time of the transients and the power consumption through resistors 106.